Field of The Invention:
The present invention relates to a configuration for a power supply of a component in an exhaust gas system, wherein in particular a power supply for an electrode for producing an electrical field in the exhaust gas system is specified.
A multiplicity of different concepts for eliminating soot particles from exhaust gases in mobile internal combustion engines, have already been discussed. In addition to wall flow filters which are closed on alternate sides, open secondary flow filters and gravity precipitators, etc., systems have also already been proposed in which the particles in the exhaust gas are electrically charged and then precipitated using electrostatic attraction forces. Those systems are known, in particular, by the designation “electrostatic filter” or “electric filter.”
For such electric filters, (a plurality of) discharge electrodes and collector electrodes positioned in the exhaust gas line are generally proposed. In that context, for example, a central discharge electrode which runs approximately centrally through the exhaust gas line and a surrounding lateral surface of the exhaust gas line as a collector electrode, are used to form a capacitor. With that configuration of the discharge electrode and of the collector electrode, an electrical field is formed transversely with respect to the direction of flow of the exhaust gas, wherein the discharge electrode can be operated, for example, with a high voltage which is in the region of approximately 15 kV. As a result, in particular, corona discharges can form by which the particles flowing with the exhaust gas through the electrical field are charged in a unipolar fashion. Due to that charge, the particles migrate to the collector electrode as a result of the electrostatic Coulomb forces.
In addition to systems in which the exhaust gas line is embodied as a collector electrode, systems are also known in which the collector electrode is embodied, for example, as a wire mesh. In that context, the accumulation of particles on the wire mesh serves the purpose, under certain circumstances, of combining the particles with further particles in order to thereby achieve an agglomeration. The exhaust gas which flows through the mesh then carries the relatively large particle agglomerates along with it and feeds them to classic filter systems.
Even if the systems described above have heretofore proven suitable, at least in trials, for the treatment of soot particles, the implementation of that concept for series operation in motor vehicles still constitutes a large technical challenge. That applies, in particular, with respect to the greatly fluctuating soot load, which is very high at times, in the exhaust gas. Likewise, the desired retrofitability of such a system for use in exhaust gas systems which exist at present still constitutes a large problem. In particular, quantities of exhaust gas which generally increase suddenly occur in the exhaust gas system of motor vehicles, and do not occur, for example, in stationary internal combustion engines which are used to generate electrical power. Furthermore, the exhaust gas systems are subject to mechanical loading, for example due to unevennesses of the ground. In addition, it is necessary to bear in mind the fact that in view of the increased power and/or effectiveness of such exhaust gas systems it is also necessary to regenerate the filter systems (periodically and/or continuously) in order to eliminate soot particles, with the regeneration involving the conversion of the soot into gaseous components.
When filter systems are regenerated, it is also known not only to perform intermittent regeneration by brief heating, that is to say burning the soot (catalytically motivated, oxidative conversion), but also to convert the soot by nitrogen dioxide (NO2). The advantage of the continuous regeneration with nitrogen dioxide is that the soot can then already be converted at significantly lower temperatures (in particular less than 250° C.). For that reason, continuous regeneration is preferred in many application cases. However, that leads to the problem that it is necessary to ensure that the nitrogen dioxide in the exhaust gas comes into contact with the accumulated soot particles to a sufficient extent.
In that context as well, technical difficulties arise in the implementation of continuous operation of such exhaust gas systems in motor vehicles, wherein the different loading of the internal combustion engines gives rise to different exhaust gas flows, compositions of exhaust gas and/or temperatures.
Furthermore, it is to be borne in mind that when such components are made available for such a soot precipitation system, simple components are to be used as far as possible, in particular components which can be manufactured cost-effectively as part of series production as well. Furthermore, particularly with respect to the construction of the electrodes, it is necessary to bear in mind that under certain circumstances they have to be positioned so as to be aligned in the exhaust gas line, in particular in such a way that an undesirably high ram pressure or undesired eddying of the exhaust gas does not occur in the region of the electrode.
When such an electrical field is formed, it is also necessary to ensure that the voltages and currents which are necessary therefor are reliably made available on a continuous basis and, in particular, danger to the surroundings or to persons is precluded. In that context it is necessary to bear in mind that to a certain extent voltages in the range of 1 to 30 kV are to be implemented, wherein the currents are generally relatively low, for example less than 0.1 ampere.